Radio frequency (“RF”) signal receivers must distinguish between a primary or desired signal and any interfering signal. In some instances, the interfering signal unintentionally results from adjacent communication channels overflowing into the desired communication channel. Additionally, the usable radio spectrum is highly populated, and occupied communication channels can potentially act as interferers within a desired wideband communication channel. In other instances, such as radar detection systems, the interference may be intentionally applied as a jamming or electronic counter measures signal designed to prevent acquisition of the primary or desired signal.
Many methods are known to suppress interfering signals. Known methods use discrete components to implement a time delay to an interfering signal, and then apply summation components to cancel the interfering signal. As a non-limiting example, U.S. Pat. No. 4,739,518 discloses a method of interference suppression that utilizes a direct down-conversion of the received signal, which is then divided into two separate RF signals. The RF signals are fed along two complimentary paths, where one signal is limited in amplitude and the other is amplified and delayed. The two signals are then subtracted from one another, greatly reducing the interfering signal while only slightly affecting the desired portion of the received signal.
The most common approaches to interference suppression provide filtering of the signal to suppress interference, particularly in instances where poor isolation between the transmit path and the receive path in a communication system causes leakage of the transmit path to the receive path. Thus, for example, band-pass filters and bond-wire inductors are used to filter out interference caused by jammers and transmit path leakage. In general, such filtering methods are only feasible for low frequency operations, and are limited by the low quality factors of integrated inductors and capacitors used to create the filtering.
Complex notch filtering is also known. U.S. Pat. No. 5,592,178 discloses a method that applies a predetermined complex weight in terms of amplitude and phase to each transmit/receive module at the element level to produce a notch in the spectrum in the direction of the interfering signal. The notch is controlled using complex digital signal processing control logic applied using multiple discrete components. Specifically, time delay units and phase shift circuits are incorporated separately in two subsystems. When a time delay is required, the time delay unit is adjusted, which has the effect of inducing a phase change. As a result, the phase shift circuits in the other sub-system must be adjusted to compensate for the change in the time delay unit.
Recently, the digital signal processing has become increasingly complex. U.S. Pat. No. 7,483,711 discloses an interference suppression method that suppresses interference through complex sampling and modeling of a communication channel with interference. The model then returns an optimal waveform to a network node using complex digital signal processing, filtering and waveform generation to return a spectrum free of interference. Multiple different components and test equipment are utilized to provide the complicated interference suppression.
It is therefore desirable to develop a system and method for interference suppression that eliminates the need for filtering and for complicated digital signal processing and modeling while minimizing the complexity of the system. It is also desirable that the system and method be implemented without requiring multiple discrete components, both to reduce cost and to minimize the size and power requirements of the interference suppression system and method.